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A  Study  of  the  Semi-Permeable   Membranes  of 
Zinc  Ferrocyanide  and  of  Copper  Cobalticyanide 


DISSERTATION 

Submitted  to  the  Board  of  University  Studies 
of  the  Johns  Hopkins  University  in  conformity 
with  the  Requirements  for  the  Degree  of 
Doctor  of  Philosophy 


BY 


ARTHUR  DUNHAM  HOLMES 


1911 


PRESS  or 
FOSNOT    &    WILLIAMS    CO. 

514-616   W.    FRANKLIN    ST. 
BALTIMORE,    MD 


A  Study  of  the  Semi-Permeable    Membranes  of 
Zinc  Ferrocyanide  and  of  Copper  Cobalticyanide 


DISSERTATION 

Submitted  to  the  Board  of  University  Studies 
of  the  Johns  Hopkins  University  in  conformity 
with  the  Requirements  for  the  Degree  of 
Doctor  of  Philosophy 


BY 

ARTHUR  DUNHAM  HOLMES 

1911 


CONTENTS. 

Page. 
Acknowledgment 3 

Introduction 5 

Zinc  Ferrocyanide  Membrane 6 

Experimental : 

Cell  Zn    I 7 

Cell  Znll , 12 

Conclusions , 18 

Copper  Cobalticyanide  M embrane 18 

Experimental: 

Cell  Coi 20 

Cell   Co4 22 

Conclusions 25 

Removal  of  Mejnjb*qanes_4_,'_  ^_,«.j.-*- 25 


Biographical 


.28 


ACKNOWLEDGMENT. 

The  author  desires  to  express  his  gratitude  to  President 
Remsen,  Professor  Morse,  Professor  Jones,  Associate  Pro- 
fessor Acree,  Professor  Renouf,  and  Professor  Swartz  for 
instruction  in  the  lecture  room  and  in  the  laboratory. 

The  author  further  wishes  to  especially  thank  Professor 
Morse,  under  whose  supervision  this  investigation  was  carried 
out,  for  his  very  many  timely  and  valuable  suggestions. 


222273 


INTRODUCTION. 

Ten  years  ago  it  was  discovered  in  this  laboratory1  that 
semi-permeable  membranes  could  be  deposited  very  satisfac- 
torily by  means  of  the  electrolytic  method.  Several  membranes 
which  were  depositen  at  that  time  by  this  process  proved  to  be 
quite  active.  When  tested  by  the  methods  then  available, 
they  appeared  to  be  quite  promising.  However,  none  of  them 
with  the  exception  of  the  previously  well  known  copper  ferro- 
cyanide  membrane  were  extensively  investigated.  In  fact  no 
thorough  investigation  was  possible  until  the  problem  of  pro- 
ducing satisfactory  porous  cells  had  been  solved.  Later,  when 
the  problem  had  been  satisfactorily  worked  out  the  supply  of 
good  cells  was  too  limited  to  justify  the  sacrifice  of  any  of 
them  for  the  investigation  of  membranes  of  unproved  excell- 
ence. Recently,  however,  the  supply  of  cells  reached  the  point 
where  a  portion  of  them  could  be  devoted  to  this  purpose. 
Hence  the  investigation  of  a  number  of  the  membranes  which 
were  then  electrolytically  depoited  has  been  resumed.  The 
investigation  that  was  undertaken  by  the  author  was  that  of 
zinc  ferrocyanide. 

Tammann  was  the  first  to  observe  that  this  substance  is 
osmotically  active.  His  work  along  this  line  was  limited  to 
the  ferrocyanides  of  copper  and  zinc.  He  used  the  so-called 
optical  method  which  consisted  in  allowing  a  drop  of  copper 
or  zinc  sulphate  to  fall  into  a  solution  of  potassium  ferrocyan- 
ide. This  drop  is  immediately  surrounded  by  a  film  of  copper 
or  zinc  ferrocyanide.  The  passage  of  water  through  this  film 
is  always,  of  course  from  the  more  dilute  to  the  more  concen- 
trated solution.  Hence  the  drop  will  swell  or  shrink  accord- 
ing as  the  solution  within  it  is  more  or  less  dilute  than  the 
solution  which  surrounds  it.  Thus  by  observing  the  currents 
about  the  drop  Tammann  was  able  to  determine  the  relative 
concentrations  of  the  two  solutions. 

The  earliest  investigations  of  the  electrolytically  deposited 
zinc  ferrocyanide  membrane  was  made  in  this  laboratory  by 
B.  F.  Carver2  in  1903.  After  showing  that  this  membrane 
could  be  deposited  electrolytically  by  the  method  of  Morse  & 
Horn3  Carver  studied  its  osmotic  activity  measured  in  terms 
of  the  rate  of  endosmose.  This  was  determined  by  measuring 
the  amount  of  solution  delivered  from  a  cell  in  which  the 
membrane  was  deposited.  In  some  cases  he  measured  the 
pressure  developed  by  attaching  an  open  manometer  to  the 
cell.  However,  it  has  been  shown  on  many  occasions  that  it 
is  impossible  to  measure  correctly  osmotic  pressure  with  cells 

1  Amer.  Chem,  Jour.  26,  80. 

2  B.  F    Carver  Dissertation  Johns  Hopkins  Univ.,  1903. 

3  Amer.  Chem.  Jour.  26,  80. 


such  as  were  available  at  the  time  when  Carver  did  his  work . 
Consequently,  it  must  be  remembered  that  experiments  of  this 
nature  merely  indicate  the  osmotic  activity  at  low  pressures, 
and  do  not  in  the  least  indicate  its  power  to  withstand  higher 
pressures. 

Three  years  later  W.  L,.  Kennon1  took  up  the  study  of 
the  zinc  ferrocyanide  membrane,  And  although  Kennon  did 
his  work  with  better  cells  he  did  not  carry  his  investigation 
far  enough  to  determine  whether  the  failure  to  obtain  satisfac- 
tory results  was  due  exclusively  to  a  defective  membrane  or  in 
part  to  defective  cells.  Kennon  speaks  of  the  zinc  ferrocyan- 
ide membrane  in  the  following  language.  "However,  the 
membrane  deposited  under  the  conditions  employed  in  this 
work  seem  unsuitable  for  the  measurement  of  osmotic  pres- 
sures. *  *  The  results  obtained  hardly  seem  capable  of 
explanation  on  any  other  basis  than  that  the  membrane  does 
not  adhere  firmly  to  the  cell  wall.  *  *  Again,  the  ease  with 
which  the  membrane  could  be  detached  from  the  cell  by  simple 
agitation  with  water  is  a  further  indication  of  the  imperfect 
manner  in  which  it  is  attached  to  the  cell  wall.  It 
might  therefore  be  concluded  that  zinc  ferrocyanide  deposited 
under  the  conditions  employed  in  this  work,  cannot  be  de- 
posited on  the  rather  dense  walls  of  the  cells  used,  in  a  form 
suitable  for  the  measurement  of  high  osmotic  pressures."  In 
as  much  as  since  Kennon 's  time  the  cells  have  been  improved 
in  many  ways  it  was  suggested  that  the  author  resume  the  in- 
vestigation of  the  zinc  ferrocyanide  membrane,  to  ascertain 
with  greater  certainty  whether  it  is  suitable  for  the  measure- 
ment of  osmotic  pressure. 


ZINC  FERROCYANIDE  MEMBRANE 

Zinc  ferrocyanide,  Zn2  Fe(CN)e  3H2O,  is  formed  as  a 
heavy,  white,  gelatinous  precipitate  when  aqueous  solutions  of 
zinc  sulphate  and  potassium  ferrocyanide  are  mixed.  It  is 
insoluble  in  water  and  little  soluble  in  the  dilute  mineral  acids. 
It  is  however  soluble  in  the  caustic  alkalis. 

The  type  of  cell  used  in  this  investigation  was  that  now 
commonly  used  in  this  laboratory,  which  was  described  in  the 
American  Chemical  Journal,  Vol.  45,  page  111.  Before  de- 
positing a  membrane  in  a  cell  it  is  necessary  to  remove  all  the 
air  enclosed  in  the  minute  pores  of  the  cell  wall.  This  was 
done  in  the  usual  manner  by  electrical  endosmose  with  a  .005 
normal  solution  of  lithium  sulphate.  The  cell  was  surrounded 
by  an  anode  and  contained  within  a  cathode,  both  electrodes 


1     W.  L.  Kennon  Dissertation  Johns  Hopkins  Univ.,  19O6. 


being  of  platinum.  At  intervals  the  electrolysis  was  stopped 
and  the  solutions  on  the  exterior  and  interior  of  the  cell  were 
thoroughly  mixed.  When  it  was  considered  that  the  air  had 
been  entirely  removed,  the  cell  was  taken  out  emptied  and 
rinsed  with  water.  The  cell  was  then  soaked  for  a  time  in 
distilled  water.  Afterwards  the  minute  quantity  of  electrolyte 
still  remaining  within  the  cell  wall  was  removed  by  continuing 
the  electrolysis  with  the  use  of  distilled  water.  When  the 
resistance  had  become  equivalent  to  the  resistance  of  distilled 
water  the  cell  was  considered  as  ready  for  the  deposition  of 
the  membrane. 

In  the  deposition  of  the  membrane  the  cell,  surrounded 
by  a  metallic  cylinder  which  serves  as  an  anode,  is  placed  in 
a  glass  vessel.  Within  the  cell  is  a  platinum  cylinder  which 
serves  as  the  cathode.  The  cell  is  closed  by  a  rubber  stopper 
through  which  pass  an  overflow  tube,  a  funnel  which  reaches 
nearly  to  the  bottom  of  the  cell  and  the  wire  leading  to  the 
cathode.  After  closing  the  circuit  the  appropriate  solutions 
are  poured  simultaneously  hit  3  the  cell  and  into  the  vessel  in 
which  the  cell  is  placed. 

In  this  investigation  of  the  zinc  ferrocyanide  membrane 
two  cells  designated  Zn  I.  and  Zn  II.  were  used.  And 
although  the  work  with  these  two  cells  was  carried  on  simul- 
taneously and  under  exactly  the  same  conditions  the  conduct 
of  each  will  be  considered  separately. 

EXPERIMENTAL  PART 

CELL  ZN  I. 

Cell  Zn  I.  was  subjected  to  electrical  endosmose  with  a 
.005  normal  solution  of  lithium  sulphate  for  a  period  of  four 
and  one  quarter  hours,  during  which  time  59cc.  of  the  lithium 
sulphate  solution  passed  from  the  exterior  to  the  interior  of 
the  cell.  A  109  volt  current  was  used  for  this  purpose.  The 
resistance  offered  by  the  cell  with  the  electrolyte  was  approxi- 
mately 10,000  ohms.  After  the  air  had  been  completely 
removed  in  the  manner  described,  the  solution  of  the  elec- 
trolyte was  replaced  by  distilled  water  and  the  electrolysis 
continued  with  frequent  renewal  of  the  water.  The  removing 
of  the  electrolyte  required  about  forty  hours.  During  this 
time  the  resistance  rose  uniformally  from  7,100  ohms  •  to 
39,600  ohms,  at  which  point  it  remained  practically  constant. 
The  conductivity  having  become  constant,  it  was  considered 
that  the  electrolyte  was  entirely  removed  from  the  wall  of  the 
cell.  The  preliminary  work  of  removing  the  air  and  after 
that  the  electrolyte  from  the  cell  wall  extended  over  a  period 
of  twelve  days. 


8 

The  deposition  of  the  zinc  ferrocyanide  membrane  in  cell 
Zn  I.  was  commenced  on  October  26.  The  method  of  its 
deposition  and  development  was  essentially  the  same  as  the 
method  already  described.  The  cell,  surrounded  by  an  anode 
of  zinc  and  containing  within  it  a  cathode  of  platinum  was 
placed  in  a  glass  vessel.  Within  the  cell  was  placed  a  solution 
of  potassium  ferrocyanide  and  in  the  glass  containing  the  cell 
was  placed  a  solution  of  zinc  sulphate.  The  zinc  sulphate 
and  potassium  ferrocyanide  solutions  used  in  this  connection 
were  one  tenth  osmotically  normal,  due  allowance  being  made 
for  the  dissociation  of  the  two  salts.  In  using  potassium 
ferrocyanide  in  the  electrolytic  deposition  of  the  ferrocyanide 
membranes,  potassium  hydroxide  is  always  formed  by  a  de- 
composition of  the  potassium  ferrocyanide.  Consequently,  in 
order  to  prevent  decomposition  of  the  zinc  ferrocyanide  mem- 
brane, by  the  potassium  hydroxide  formed,  a  very  frequent 
renewing  of  the  potassium  ferrocyanide  solution  is  necessary. 
In  this  work  the  solution  within  the  cell  was  renewed  at  in- 
tervals of  three  minutes.  The  resistance  of  the  membrane 
was  determined  once  in  six  minutes. 

Perhaps  the  best  manner  in  which  a  brief  history  of  the 
initial  deposition  of  the  membrane  can  be  given  is  by  means 
of  a  table.  In  this  table  simply  a  statement  of  the  length  of 
the  period  of  deposition  and  of  the  maximum  resistance 
obtained  during  that  period  will  be  given. 

Maximum  resistance 
October  26      3.06  P.  M.—  4.42  P.  M.  28,590  ohms 

27  10.51  A.  M.— 12.28  P.  M.  37,883 

3.05  P.  M.—  4.55  P.  M.  54,285 

28  3.00  P.  M.—  4.10  P.  M.      38,000 
31  11.33  A.  M.— 12.37  P.  M.      37,666 

2.48  P.  M.—  4.29  P.  M.      41,851 
Nov.    1   2.45  P.  M.—  4.35  P.  M.      34,242 

2  11.45  A.  M.— 12.43  P.  M.      46,818 

2.25  P.  M.—  4.30  P.  M.      59,210 

3  11. 08  A.  M.— 12.31  P.  M.  58,947 
9    10.45  A.  M.— 11.11  P.  M.             62,111 

3.12  P.  M.—  4.36  P.  M.  74,666 

10  11.12  A.M.— 12.32  P.  M.  83,571 

14  11.07  A.  M.— 12.03  P.  M.  70,000 

3.11  P.  M.—  4.32  P.  M.  93,750 

22  11. 15  A.  M.— 12. 34  P.  M.  84,630 

29  10.47  A.  M.— 12.15  P.  M.  84,630 

It  was  noticed  that  in  each  instance  during  the  first  few 
minutes  of  membrane  deposition  the  resistance  increased  very 
radidly.  Also  it  was  noted  that  the  longer  the  period  of  soak- 


ing  of  the  membrane  in  pure  water,  the  lower  the  initial  re- 
sistance and  the  more  rapid  the  rise  of  the  resistance  during 
the  first  five  or  ten  minutes  of  membrane  deposition.  It  has 
been  suggested  that  this  rapid  rise  in  the  resistance  of  the 
membrane  may  be  due  to  the  membrane  assuming,  while  being 
soked  in  water  in  the  absence  of  an  electolyte,  a  more  colloidal 
state.  Then  when  the  electrolytes  in  subsequent  strengthen- 
ing of  the  membrane  are  brought  by  the  current  in  close  prox- 
imity to  the  membrane  a  much  denser  packing  of  the  mem- 
brane results.  If  this  is  the  true  explanation  of  the  phenomena, 
then  it  is  easy  to  see  why  a  long  soaking  is  followed  by  a 
greater  and  quicker  rise  in  resistance  than  is  a  shorter  period 
of  soaking. 

Another  interesting  feature  of  this  membrane  was  the  ap- 
pearance during  the  deposition,  of  patches  of  membrane  of 
unusual  thickness.  These  were  formed  generally  at  the  point 
where  the  glazed  and  unglazed,  interior  portions  of  the  cell 
met.  The  first  appearance  of  these  patches  was  on  November 
1.  At  that  time  the  cell  had  been  subjected  to  the  membrane 
forming  process  for  four  days.  These  patches  were  carefully 
removed  by  rubbing  the  interior  cell  wall  at  the  point  where 
they  were  formed  with  a  soft  cloth.  The  only  result  following 
their  removal  which  was  noted  was  a  subsequent  slight  in- 
crease in  the  resistance  of  the  membrane.  Again  two  days 
later  there  was  noticed  other  patches  similar  to  the  first  in  ap- 
proximately the  same  position.  These  were  not  removed  at 
this  time  and  the  only  apparent  difference  between  the  mem- 
brance  in  cell  Zn  I  and  cell  Zn  II  which  did  not  have  any 
patches  at  this  time  was  perhaps  a  slightly  lower  resistance. 
And  there  is  no  direct  evidence  that  even  this  difference  was 
caused  by  these  patches.  About  a  week  later  the  patches  were 
again  removed  in  the  manner  already  described.  Two  weeks 
later  patches  appeared  in  both  cells  at  the  junction  of  the 
glazed  and  unglazed  portions.  These  were  not  removed  and 
the  cell  was  set  up  for  measurement  with  the  patches  on  the 
interior  wall.  After  the  cell  was  taken  down  the  patches  did 
not  appear  as  large,  and  never  appeared  to  increase  in  size 
although  the  cell  was  set  up  for  measurements  and  also  sub- 
jected to  the  membrane  forming  process  repeatedly  after  this 
time.  There  are  several  possible  explanations  for  the  forma- 
tion of  these  patches.  However,  in  spite  of  that  fact  it  would 
be  difficult  to  satisfactorily  explain  why  these  should  occur. 

EXPERIMENT  I. 

Cell  Zn  I.  was  set  up  for  the  first  measurement  at  3.05  P. 
M.,  November  29,  its  resistance  being  84,630  ohms.  A  weight 


10 

normal  cane  sugar  solution  was  used .  The  sugar  solution  was 
made  osmotically  normal  with  respect  to  potassium  ferrocya- 
nide,  while  the  solution  surrounding  the  cell  was  made  one 
hundredth  normal  with  respect  to  zinc  sulphate.  The  cell 
was  set  up  at  twenty-five  degrees,  which  is  the  temperature  at 
which  the  membrane  was  deposited.  The  initial  rise  of  the 
mercury  in  the  manometer  was  watched  very  closely,  and  rate 
of  rise  was  as  follows: — 

3.05  P.  M.  mercury  at  0. 

3.16  P.  M.  had  risen    62.0  mm. 

3.23P.M.  111.0 

3. 33  P.  M.  "            "       "      181.0    " 
3.39  P.  M.  222.0 
3.45  P.  M.  256.0 
3.55  P.  M.  305.0 
4.05  P.  M.  336.0 

4. 16  P.  M.  354.0 

4.27P.M.  361.0 

4.34  P.  M.  365.0 

The  total  length  of  the  original  nitrogen  column  in  the 
manometer  was  445.43  mm.  Since  the  rise  of  the  mercury 
column  was  apparently  perfectly  continuous  there  was  either 
no  leakage  of  the  membrane  or  the  increase  in  the  osmotic 
pressure  was  more  rapid  than  the  leakage.  Otherwise  there 
would  have  been  either  a  halt  in  the  ascent  of  the  miniscus  or 
a  positive  falling  of  the  same.  Also,  as  will  be  noted  in  this 
brief  table,  the  rise  of  the  mercury  was  very  rapid,  which  in- 
dicates, as  has  previous  work  with  this  membrane,  that  it  is 
very  active. 

After  these  preliminary  observations  the  cell  was  placed 
in  a  constant  temperature  bath.  The  pressure  continued  to 
rise  uniformly  until  1  P.  M.  November  30,  at  which  time  it 
reached  3.39  atmospheres,  the  maximum  pressure  which  was 
obtained  for  this  experiment.  The  pressure  of  the  normal 
solution  of  cane  sugar  is  known  from  other  work  to  be  27.223  at- 
mospheres at  this  temperature.  The  pressure  then  began  to 
slowly  fall,  being  at  5  P.  M.  3.36  atmospheres,  at  10  P.  M.  3.33 
atmospheres,  and  at  10  A.  M.  the  next  day  3.28  atmospheres. 
From  the  constant  decrease  in  pressure  it  was  evident  that 
there  was  a  leakage  of  the  membrane.  Consequently  the  cell 
was  taken  down.  The  sugar  solution  taken  from  the  cell  was 
of  a  blue  tinge  and  ,so  dark  that  it  was  impossible  to  read  its 
rotation  in  the  saccharimeter.  However,  there  must  have 
been  a  loss  in  rotation,  for  the  solution  was  undoubtedly 
diluted. 


11 

On  taking  down,  the  cell  was  placed  in  a  saturated  solu- 
tion of  thymol  and  allowed  to  soak  for  forty-eight  hours.  On 
December  4  the  cell  was  again  subjected  to  the  membrane- 
forming  process.  The  resistance  at  first  was  very  low,  being 
only  17,833  ohms.  However,  the  resistance  gradually  rose 
until  it  reached  82,307  ohms.  The  cell  was  then  again  soaked 
in  a  saturated -thymol  solution.  On  December  5  the  membrane 
was  reinforced,  the  resistance  being  at  the  start  27,894  ohms; 
at  the  end  of  five  minutes  it  had  risen  to  46,087  ohms,  and  from 
that  point  the  resistance  gradually  rose  to  116,000  ohms.  On 
December  6  the  membrane  was  once  more  reinforced,  this  time 
for  a  period  of  an  hour,  its  maximum  resistance  for  this  period 
being  116,000  ohms. 

EXPERIMENT  II. 

Cell  Zn  I.  was  again  set  up  at  4  P.  M.  December  6.  Its 
resistance  was  116,000  ohms.  As  in  the  previous  experiment  a 
weight  normal  cane  sugar  solution  was  used.  Also  hundredth 
normal  solutions  of  zinc  sulphate  and  potassium  ferrocyanide 
were  used  as  membrane  menders.  The  pressure  rose  uni- 
formly, though  less  rapidly  than  in  the  former  experiment, 
until  10  A.  M.  December  7,  at  which  time  it  was  1.52  atmos- 
pheres. The  pressure  then  fell  constantly  for  twenty-four 
hours,  after  which  time  the  cell  was  taken  down.  The  solution 
taken  from  the  cell  was  too  cloudy  to  read  the  rotation  in  the 
saccharimeter.  The  precipitate,  which  rendered  the  solution 
cloudy,  was  extremely  slow  in  subsiding,  so  that  even  after 
two  days  it  was  not  practical  to  determine  the  rotation  of  the 
solution.  However,  considering  the  low  pressure,  the  dilu- 
tion must  have  been  quite  large.  The  cell  was  soaked  in 
saturated  thymol  solution  for  two  days,  after  which  the  mem- 
brane was  again  reinforced.  The  initial  resistance  after  the 
soaking  was  53,250  ohms,  which  gradually  rose  to  106,500 
ohms.  The  cell  was  then  soaked  for  two  weeks,  when  the 
membrane  was  again  reinforced;  the  maximum  resistance 
now  being  100,000  ohms. 

EXPERIMENT  III. 

Cell  Zn  I.  was  set  up  on  January  4,  at  4  P.  M.  The 
resistance  was  100,000  ohms.  A  weight  normal  sugar  solu- 
tion was  used,  with  hundredth  normal  solutions  of  zinc  sul- 
phate and  potassium  ferrocyanide  as  membrane  menders.  The 
mercury  rose  slowly  until  9  P.  M.,  but  not  far  enough  to 
come  within  the  range  of  the  telescope  on  the  cathetometer. 
At  9  A.  M.  the  following  day  the  mercury  had  dropped  to 
atmospheric  pressure  and  it  did  not  rise  again  although  the 
cell  remained  iu  the  bath  for  forty-eight  hours  longer.  The 


12 

cell  was  then  taken  down.  The  loss  in  rotation  showed  that 
there  had  been  considerable  dilution  and  consequently  con- 
siderable leaking  of  the  membrane.  After  soaking  for  two 
days  the  membrane  was  again  reinforced.  The  resistance  at 
the  start  was  14,705  ohms  and  gradually  rose  to  83,384  ohms. 

EXPERIMENT  IV. 

Cell  Zn  I.  was  set  up  on  January  13,  at  12  o'clock. 
Weight  normal  sugar  solutions  and  hundredth  normal  solu- 
tions of  zinc  sulphate  and  potassium  ferrocyanide  as  mem- 
brane menders  were  used.  The  final  resistance  was  83,384 
ohms.  The  cell  was  in  the  bath  for  three  days  and  at  no  time 
could  any  rise  in  the  mercury  be  perceived.  Consequently 
there  was  no  pressure  developed.  On  taking  down  the  cell 
the  solution  showed  a  large  loss  in  rotation  indicating  a  con- 
siderable dilution. 

CELL  ZN  II. 

Since  the  deposition  of  the  zinc  ferrocyanide  membrane  in 
Cell  Zn  II.  was  essentially  the  same  as  in  the  case  of  Cell  Zn 
I.  only  a  brief  statement  of  the  preliminary  work  need  be 
given.  A  .005  normal  solution  of  lithium  sulphate  was  used 
for  the  removal  of  the  air.  The  endosmose  was  121cc.  in  four 
hours,  with  a  maximum  resistance  of  8,384  ohms.  In  the  re- 
moval of  the  electrolyte  from  the  cell  wall  which  required 
approximately  forty  hours  a  maximum  resistance  of  56,000 
ohms  was  obtained.  In  reporting  in  connection  with  the 
deposition  of  the  membrane  in  Cell  Zn  II.,  simply  a  statement 
of  the  length  of  each  period  of  membrane  deposition  and  of 
the  maximum  resistance  obtained  during  that  period  will  be 
given  in  tabular  form. 


Maximum  resistance 

October  26 

5 

.06 

P. 

M.—  4.42 

P. 

M. 

28,3/^5  ohms 

M 

27 

10 

.51 

A. 

M. 

—12.28 

P. 

M. 

37,833 

11 

3 

.05 

P. 

M. 

—  4. 

55 

P. 

M. 

54, 

285 

'  ' 

28 

3 

.00 

P. 

M.—  4.10 

P. 

M. 

38, 

000     " 

*  ' 

31 

11 

.33 

A. 

M. 

—12.37 

P. 

M. 

37,666 

'  ' 

2 

.48 

P. 

M. 

—  4. 

29 

P. 

M. 

41, 

851 

Nov. 

1 

2 

.54 

P. 

M. 

—  4. 

35 

P. 

M.     > 

30, 

432 

2 

11. 

45 

A. 

M. 

—12. 

43 

P. 

M. 

55, 

500 

':' 

2, 

,25 

P. 

M. 

—  4. 

30 

P. 

M. 

75, 

333 

i  < 

3 

11. 

08 

A. 

M. 

—12. 

30 

P. 

M. 

74, 

666 

'  ' 

9 

10. 

45 

A. 

M. 

—  12.11 

P. 

M. 

58, 

947 

3.12 

P. 

M. 

—  4. 

36 

P. 

M. 

74, 

665 

<  c 

10 

11, 

.12 

A. 

M. 

—12. 

32 

P. 

M. 

65, 

000 

i  < 

14 

11.07 

A. 

M. 

—12. 

03 

P. 

M. 

70, 

000 

i  < 

29 

10.47 

A. 

M. 

—12. 

15 

P. 

M. 

73, 

000 

13 

EXPERIMENT  I. 

Cell  Zn  II.  was  set  up  for  the  first  measurement  Novem- 
ber 29,  at  3.00  P.  M.  A  weight  normal  cane  sugar  solution 
was  used,  with  hundredth  normal  solutions  of  zinc  sulphate 
and  potassium  ferrocyanide  as  membrane  menders.  The  re- 
sistance was  73,333  ohms.  In  all  of  the  work  with  cell  Zn  II. 
the  temperature  was  25°.  The  record  of  the  initial  rise  of 
mercury  in  the  manometer  is  as  follows: 

3.11  P.  M.  mercury  at  0 

3.21  P.  M.  had  risen  22.0  mm. 

3.33  P.  M.  56.0 

3.45  P.  M.  86.0 

3.55  P.  M.  115.0 

4.05  P.  M.  139.0 

4.16  P.  M.  162.0 

4.26  P.  M.  183.0 

The  total  length  of  the  original  nitrogen  column  in  the 
manometer  was  497.52  mm.  Since  the  rise  in  pressure  was 
continuous  there  could  have  been  either  no  break  in  the 
membrane  or  the  leakage  was  slower  than  the  increase  in 
osmotic  pressure.  In  this  case  as  in  the  first  experiment  with 
cell  Zn  I.  it  was  shown  that  fresh  zinc  ferrocyanide  is  a  very 
active  membrane.  During  the  observations  noted  in  the  above 
table  the  cell  was  in  a  constant  temperature  bath  while  the 
manometer  was  exposed  to  the  temperature  of  the  room  which 
was  somewhat  lower.  After  placing  the  cell  in  the  larger 
bath  the  pressure  rose  until  10  P.  M.,  at  which  time  it  was 
4.49  atmospheres,  the  maximum  pressure  for  this  experiment. 
The  pressure  then  commenced  to  drop.  It  fell  constantly  for 
thirty-six  hours  at  the  end  of  which  time  the  cell  was  taken 
down.  The  solution  taken  from  the  cell  was  of  a  greenish 
blue  color  and  too  cloudy  to  permit  a  determination  of  its  rota- 
tion. However,  there  must  have  been  a  decided  loss  in  con- 
centration. The  cell  was  soaked  out  and  the  membrane  rein- 
forced in  the  manner  heretofore  described,  the  maximum 
resistance  obtained  being  98,636  ohms. 

EXPERIMENT  II. 

Cell  Zn  II.  was  again  set  up  on  December  13,  at  11.30  A. 
M.,  with  a  weight  normal  solution  of  cane  sugar.  Hundredth 
normal  solutions  of  zinc  sulphate  and  potassium  ferrocyanide 
were  used  as  membrane  menders.  The  resistance  at  this  time 
was  98,636  ohms.  The  mercury  rose  about  an  inch  in  the 
manometer  and  remained  there  for  two  days.  After  which 
the  cell  was  taken  down.  The  solution  from  the  cell  showed 


14 

a  large  loss  in  rotation  which  indicates  that  there  was  a  con- 
siderable leakage  of  the  membrane. 

Since  the  membrane  developed  very  little  pressure,  and 
the  solution  from  the  cell  showed  a  greenish  blue  color,  it  ap- 
peared probable  that  the  membrane  had  been  affected  by 
penicillium.  It  has  been  well  established  in  the  work  on  the 
copper  ferrocyanide  membrane  that  penicillium  not  only  ruins 
a  membrane  containing  nitrogen,  but  that  it  also  produces  a 
greenish  blue  color  in  solutions  containing  potassium  ferrocya- 
nide. On  this  account  it  was  thought  best  to  give  the  cell  a 
short  treatment  with  some  powerful  disinfectant.  Conse- 
quently on  December  17  the  cell  was  subjected  for  a  period  of 
twenty  minutes  to  concentrated  fumes  of  hydrocyanic  acid. 

This  work  was  carried  out  under  a  hood  provided  with  a 
good  draft.  The  neck  of  a  bell-jar,  which  fitted  tightly  to  a 
glass  plate,  was  closed  with  a  three-hole  rubber  stopper.  Two 
delivery  tubes  passed  through  two  of  these  holes.  These  were 
connected  with  wash  bottles.  By  applying  suction  to  one  of 
these  wash  bottles  the  bell- jar  could  be  rilled  with  a  saturated 
water  vapor.  This  atmosphere  of  saturated  water  vapor  was 
necessary  in  order  that  the  membrane  should  not  become  dry 
and  thereby  useless.  Also,  by  means  of  suction  the  bell -jar 
could  be  flushed  out  before  opening  and  thus  all  danger  from 
any  excess  of  hydrocyanic  acid  fumes  could  be  avoided. 
Through  the  third  hole  in  the  rubber  stopper  was  passed  a 
dropping  funnel.  By  means  of  this  funnel  acid  could  be 
slowly  added  to  a  beaker,  within  the  bell-jar,  which  contained 
crystals  of  potassium  cyanide.  After  this  treatment  with 
hydrocyanic  acid  fumes  the  membrane  in  cell  Zn  II.  was  rein- 
forced in  the  usual  manner,  with  a  maximum  resistance  of 
62,222  ohms.  This  cell  was  set  up  on  January  4  as  was  also 
cell  Zn  I.,  which  had  not  been  treated  with  hydrocyanic  acid 
fumes.  A  comparison  of  the  records  of  the  two  cells,  in  both 
of  which  the  greenish  blue  color  had  appeared,  and  but  one  of 
which  had  been  treated  with  hydrocyanic  acid  fumes,  shows 
that  even  a  thorough  disinfection  did  not  suffice  to  greatly 
improve  the  membrane. 

EXPERIMENT  III. 

Cell  Zn  II.  was  set  up  at  4  P.  M.  January  4,  its  resistance 
being  62,222  ohms.  A  weight  normal  sugar  solution  and  hun- 
dreth  normal  solutions  of  zinc  sulphate  and  postassium  ferro- 
cyanide as  membrane  menders  were  used.  At  4.35  the 
mercury  in  the  manometer  had  risen  about  an  inch.  At  9.30 
P.  M.  the  mercury  was  apparently  in  the  same  position.  At 
9  A.  M.  the  following  day  the  mercury  had  dropped  to  atmos- 


15 


pheric  pressure  and  remained  there  for  two  days,  after  which 
the  cell  was  taken  down.  The  solution  taken  from  the  cell 
showed,  as  would  be  expected,  a  very  considerable  dilution. 
However,  it  did  not  exhibit  the  greenish  blue  color,  proving 
that  the  treatment  with  hydrocyanic  acid  fumes  in  all  proba- 
bility had  killed  the  penicillium. 

It  was  concluded  that  it  was  useless  to  experiment  further 
with  zinc  ferrocyanide  membranes.  And  it  was  suggested  to 
the  author  that  an  attempt  be  made  to  remove  this  membrane 
and  to  substitute  it  by  one  of  proved  excellence.  The  mem- 
brane selected  for  this  purpose  was  the  nickel  ferrocyanide 
membrane.  The  cells  containing  the  zinc  ferrocyanide  mem- 
brane had  been  demonstrated  to  be  thoroughly  useless  for  the 
measurements  of  osmotic  pressure.  But  it  was  not  certain 
that  the  failures  hitherto  recorded  were  due  entirely  to  the 
membrane.  In  other  words,  it  remained  to  be  proved  whether 
the  cells  were  or  were  not  of  good  quality. 

This  suggestion  was  carried  out  and  the  results  obtained 
were  quite  gratifying.  The  method  of  removing  the  zinc  ferro- 
cyanide membrane  is  taken  up  in  detail  later  in  this  paper, 
and  so  only  reference  to  it  will  be  made  here.  The  arrange- 
ments for  the  deposition  of  the  nickel  membrane  were  the 
same  as  those  already  described  except  that  an  anode  of  nickel 
was  used  and  the  cell  was  immersed  in  a  solution  of  tenth 
normal  nickel  sulphate.  The  deposition  of  the  nickel  ferro- 
cyanide membranes  in  both  cells  was  commenced  on  March  16. 
The  record  of  the  deposition  of  this  membrane  in  cells  Zn  I. 
and  Zn  II.  which  which  will  be  hereafter  designated  Nis  and 
Ni?  respectively,  is  seen  in  the  following  table.  This  table 
will  record  simply  a  statement  of  the  lengths  of  the  periods  of 
membrane  deposition  and  of  the  maximum  resistance  obtained 
during  each  period. 


Mar.  16  11.55  A.  M.— 12.30  P.  M. 

18  11.35  A.  M.— 12.10  P.  M. 

20  11.50  A.  M.— 12.20  P.  M. 

21  10.30  A.  M.— 11.23  P.  M. 

22  11.30  A.  M.— 12.08  P.  M. 

2.20  P.  M.—  3.30  P.  M. 

27  2.00  P.  M.—  3.18  P.  M. 
30  11.25  A.  M— 12.22  P.  M. 

April    1  11.45  A.  M.— 12.15  P.  M. 

5  11.25  A.  M.— 12.17  P.  M. 

7  11.25  A.  M.—  3.25  P.  M. 

12  2.30  P.  M.—  3.22  P.  M. 

28  10.25  A.  M.— 11.50  A.  M. 


Max  tnum  Resistance 
Cell  Ni?  Cell  Nis 

7,957  ohms  5,850  ohms 

16,133  20,166 

21,454  17,353 

27,143  28,387 

36,000  26,666 

37,333  28,009 

38,333  28,750 

54,272  36,773 

57,000  38,000 

52,376  30,000 

61,111  44,000 

61,111  47,817 
66,475 


56,590 

Since  these  two  cells  were  set  up  for  measurements  alter- 
nately it  perhaps  will  be  well  to  consider  the  conduct  of  each 
separately. 


16 

CEUv   NI7. 
EXPERIMENT  I. 

Cell  Nil  was  set  up  for  the  first  measurement  on  April 
28,  at  30°.  A  weight  normal  solution  was  used,  the  usual 
quantity  of  membrane  menders  also  being  added.  The  resist- 
ance of  the  cell  at  this  time  was  66,475  ohms.  The  rise  of  the 
mercury  in  the  manometer  was  closely  watched.  It  rose 
apparently  without  a  single  halt,  which  indicates  that  either 
there  was  no  leaking  of  the  membrane  or  the  leakage  if  there 
was  such,  was  less  than  the  increase  of  the  osmotic  pressure. 
The  rate  at  which  the  pressure  increased  was  phenomenal. 
At  3  P.  M.  or  after  a  period  of  three  hours  the  osmotic  pres- 
sure was  over  twenty-four  atmospheres,  the  pressure  having 
started  at  atmospheric  pressure.  At  9  P.  M.  the  pressure  had 
risen  to  over  twenty-five  atmospheres.  At  9  A.  M.  the  fol- 
lowing day  the  pressure  developed  was  25.608  atmospheres 
which  was  the  maximum  pressure  for  this  experiment.  The 
true  osmotic  pressure  of  cane  sugar  solution  at  this  tempera- 
ture and  concentration  of  solution  is  known  from  other  work 
to  be  27.223  atmospheres.  So  rapid  a  rise  from  atmospheric 
to  nearly  full  osmotic  pressure  in  so  short  a  time  is  unusual. 

After  this  maximum  pressure  had  been  obtained  the  pres- 
sure fell  uniformly  for  two  days  at  the  end  of  which  time  the 
pressure  was  24.598  atmospheres.  The  cell  was  then  taken 
down  and  placed  in  a  thymol  solution.  The  solution  taken 
from  the  cell  showed  some  loss  in  rotation.  On  May  2,  the 
membrane  was  reinforced  for  one  and  one-half  hours  during 
which  time  the  maximum  resistance  was  57,000  ohms. 


EXPERIMENT  II. 

Cell  Ni7  was  set  up  on  May  2,  at  30°.  A  weight  normal 
sugar  solution  was  used,  with  hundredth  normal  solutions  of 
nickel  sulphate  and  potassium  ferrocyanide  added  as  mem- 
brane menders.  The  pressure  rose  to  24.089  atmospheres 
during  the  first  five  hours.  At  9  A.  M.  on  the  following  day 
the  pressure  had  risen  to  24.26  atmospheres  which  was  the 
maximum  pressure  for  this  experiment.  The  pressure  re- 
mained constant  for  two  days  at  the  end  of  which  time  the 
cell  was  taken  down  and  placed  to  soak  in  a  thymol  solution. 
The  solution  taken  from  the  cell  showed  some  loss  in  rotation. 
On  May  6,  the  membrane  was  reinforced  for  one  hour,  the 
maximum  resistance  being  44,333.  On  May  8,  the  mem- 
brane was  again  reinforced  the  resistance  being  in  this  case 
73,333  ohms. 


17 

EXPERIMENT  III. 

Cell  Ni7  was  set  up  for  measurement  on  May  8,  with  a 
weight  normal  sugar  solution.  Hundredth  normal  solutions 
of  nickel  sulphate  and  of  potassium  ferrocyanide  were  added 
as  membrane  menders.  At  8  P.  M.  or  eight  hours  after 
setting  up  the  pressure  was  32.06  atmospheres.  At  10  A.  M. 
the  following  day  the  pressure  had  risen  to  32.24  atmospheres. 
The  pressure  of  thirty-two  atmospheres  is  above  that  which 
is  known  to  be  normal  for  the  solution  at  30°. 

The  explanation  of  the  over  pressure  is  to  be  found  in  the 
conditions  previous  to  the  placing  of  the  cell  in  the  bath. 
There  are  two  conditions  which  lead  to  the  development  of 
surplus  pressure  in  the  cell.  In  the  first  place  it  occurs  when- 
ever the  solution  at  the  time  of  the  setting  up  of  the  cell  is  at 
a  temperature  lower  than  that  of  the  bath  in  which  the  cell  is 
finally  placed.  The  solution,  in  this  case,  on  being  warmed 
up  to  the  temperature  of  the  bath  expands  and  produces  a 
mechanical  pressure  which  may  with  the  already  developed 
osmotic  pressure  exceed  the  true  osmotic  pressure  of  the  solu- 
tion. Whenever  this  occurs  water  should  be  discharged  from 
the  solution  through  the  membrane  resulting  in  a  slight  con- 
centration of  the  solution.  But  the  water  does  not  instant- 
aneously pass  through  the  membrane  hence  there  is  for  an  in- 
definite time  an  over  pressure  upon  the  cell  contents.  The 
second  cause  is  of  a  similar  nature.  The  temperature  of  the 
mercury  in  the  manometer  is  usually  somewhat  lower  than 
that  of  the  bath  and  this  also  expands  on  warming  up  and  may 
give  a  surplus  pressure,  if  the  placing  of  the  cell  in  the  bath 
is  delayed  for  purposes  of  observation  until  a  considerable 
osmotic  pressure  has  already  been  developed. 

CELL  NIs. 
EXPERIMENT  I. 

Cell  Nis  was  set  up  for  the  initial  measurement  on  May  5 
at  30°.  Its  resistance  was  63,333  ohms.  A  weight  normal 
sugar  solution  was  used,  the  usual  quantities  of  membrane 
menders  also  being  present.  The  rise  of  pressure  was 
even  more  rapid  than  in  the  case  of  cell  Nil.  The  pressure 
rose  in  one  and  one-quarter  hours  to  approximately  29 
atmospheres.  The  pressure  then  fell  for  two  days,  at  the  end  of 
which  time  it  was  10.98  atmospheres.  The  cell  was  then 
taken  down  and  placed  in  a  thymol  solution.  The  solution 
taken  from  the.cell  showed  a  considerable  loss  in  rotation,  in- 
dicating that  the  membrane,  though  more  active  initially,  was 
less  strong  than  that  in  the  other  cell. 


18 

The  work  of  developing  the  nickel  membranes  was  not 
carried  to  the  point  at  which  they  were  able  to  maintain  the 
maximum  osmotic  pressure  of  concentrated  solutions  for  an 
indefinite  time.  Their  further  work  was  undertaken  by  others. 
Enough  was  done,  however,  to  show  beyond  question  that  the 
general  failure  of  the  zinc  ferrocyanide  membranes  could  not 
be  due  to  imperfect  cells. 

CONCLUSIONS. 

The  results  of  the  investigation  show  : 

1.  That  the  zinc  ferrocyanide  membrane  may  be  easily 
deposited  by  the  electrolytic  method. 

2.  That  the  membrane  while  fresh  is  quite  active  and 
able  to  sustain  very  moderate  pressures. 

3.  That  the  membrane  rapidly  deteriorates  with  age,  so 
that  the  pressures  attained  on  each  succeeding  experiment  are 
lower  than  in  the  preceding  one. 

4.  That  the  membrane  after  deposition  tends  to  become 
granular.     This  tendency  is  evidenced  by  the  fact   that  the 
solutions  when  removed  from  the  cell  are  always  cloudy  in 
consequence  of  the  presence  of  suspended  zinc   ferrocyanide, 
which  has  been  detached  from  the  cell  wall.     There  can  no 
longer  be  any  doubt  that  the  zinc  ferrocyanide  membrane  is 
wholly  unsuited  to  the  measurement  of  osmotic  pressure. 

\        

THE  SEMI-PERMEABLE  MEMBRANE  OF  COPPER 
COBALTICYANIDE. 

One  of  the  many  different  electrolytically  deposited  sub- 
stances which  have  been  examined  in  this  laboratory  in  regard 
to  their  osmotic  activity  is  copper  cobalticyanide.  In  1903 
CarVer  made  a  preliminary  investigation  of  the  osmotic  activity 
of  this  substance.  It  was  shown  by  him  that  under  the  con- 
ditions of  his  work  the  copper  cobalticyanide  membrane  was 
probably  less  active  than  those  of  the  zinc  and  nickel  ferro- 
cyanides.  He  employed  potters'  cells  of  considerable  porosity 
and,  therefore,  was  unable  to  obtain  pressures  of  any  consider- 
able magnitude.  Still  he  attempted  to  measure  the  relative 
osmotic  pressures  obtained  in  the  case  of  various  membranes 
by  determining  the  height  to  which  the  solution  would  rise  in 
an  open  manometer.  He  also  measured  the  overflow  for  periods 
of  several  days.  Thus  conclusions  drawn  from  his  work  may 
not  be  entirely  conclusive. 

Three  years  later  when  far  more  perfect  cells  were  obtain- 
able a  second  investigation  of  the  copper  cobalticyanide  mem- 


19 

brane  was  carried  out  by  K.  J.  Hoffman.  In  the  introduction 
to  the  discussion  of  this  membrane  Hoffman  points  out  a  fact 
which  cannot  be  too  strongly  emphasized.  In  this  connection 
it  will  be  well  to  give  the  author's  •  exact  words,  "it  should 
be  noted  that  many  failures  to  make  direct  measurements  of 
osmotic  pressure  have  been  due,  not  to  the  membrane,  but  to 
the  faulty  character  of  the  cell  wall  in  which,  or  upon  which, 
the  membrane  was  deposited.  The  importance  of  keeping 
this  distinction  clearly  in  mind  can  not  be  urged  too  strongly, 
for  many  conclusions  reached  concerning  osmotic  pressure  and 
its  measurements  may  be  entirely  erroneous  for  no  other 
reason  than  that  the  cell  wall  did  not  provide  sufficient  sup- 
port for  the  membrane."  The  above  caution  applies  with 
special  force  to  all  early  work  upon  electrolytically  deposited 
membranes,  where  potters'  cells  were  of  a  necessity  used. 
HoffmaiT  used  a  cell  for  the  deposition  of  his  copper  cobalti- 
cyanide membrane  in  which  there  had  previously  been  one  of 
zinc  ferrocyanide.  And  his  unsatisfactory  results  may  have 
been  due  to  this  cause,  as  will  be  shown  hereafter.  It  was, 
therefore,  suggested  that  the  author  resume  the  investigation 
with  entirely  fresh  cells. 

Copper  cobalticyanide,  a  precipitate,  the  composition  of 
which  is  supposed  to  be  Cu3[Co(CN)c]2,  is  formed  when  an 
aqueous  solution  of  potassium  cobalticyanide  is  treated  with  a 
solution  of  copper  sulphate.  The  precipitate,  which  is  of  a 
turquoise  blue  color  is  insoluble  in  water  and  acids,  but  it  is 
soluble  in  ammonium  hydroxide.  It  is  also  acted  upon  by 
potassium  "hydroxide,  forming  a  green  color  which  becomes 
darker  and  finally  takes  on  the  black  appearance  characteristic 
of  cupric  oxide.  During  the  deposition  of  the  copper  cobalti- 
cyanide membrane  by  the  electrolytic  method  potassium 
hydroxide  is  formed.  In  order  to  prevent  this  from  decom- 
posing the  membrane  a  quantity  of  acetic  acid  equivalent  to 
the  potassium  is  added  to  the  cobalticyanide  solution.  In 
other  respects  the  method  employed  in  depositing  the  mem- 
brane was  the  same  as  that  employed  in  the  case  of  the  copper 
ferrocyanide  membrane.  That  is  the  anode  was  of  copper 
and  the  cathode  of  platinum.  The  solutions  were  osmotically 
of  tenth  normal  concentration.  In  the  investigation  of  cop- 
per cobalticyanide  as  a  possible  membrane  for  the  measure- 
ment of  osmotic  pressure  two  cells,  Coi  and  Coi  were  used. 
Both  cells  were  new,  that  is  no  membrane  had  been  previously 
deposited  in  them.  Since  the  preparing  of  these  cells  for  the 
deposition  of  the  membrane,  and  later  the  deposition  of 
the  membrane,  was  not  carried  simultaneously  the  history  of 
each  of  the  two  cells  will  be  given  separately. 


20, 

EXPERIMENTAL  PART. 
CELL  COi. 

The  preliminary  work  of  preparing  cell  Coi  for  the  depo- 
sition of  the  copper  cobalticyanide  membrane  was  commenced 
on  January  9.  The  cell  was  first  allowed  to  soak  in  a  .005 
normal  lithium  sulphate  solution  for  a  few  hours.  On  Janu- 
ary 10  the  cell  was  subjected  to  the  action  of  the  current  for 
two  hours.  During  this  time  32cc.  of  the  liquid  passed  through 
the  cell  wall.  The  resistance  rose  from  5,250  ohms  to  35,000 
ohms,  during  this  time.  The  cell  was  then  soaked  some  days  in 
water,  after  which  it  was  placed,  on  January  17-18,  in  distilled 
water  and  the  electrolysis  continued,  with  frequent  renewal  of 
the  distilled  water.  When  the  electrolyte  had  been  completely 
removed  from  the  cell  it  was  considered  to  be  ready  for  the 
deposition  of  the  membrane.  The  resistance  at  the  beginning 
of  the  depositions  was  18,181  ohms.  This,  however,  soon 
dropped  to  6,644  ohms,  but  during  the  next  hour  and  half  it 
rose  slowly  to  12,500  ohms.  The  subsequent  conduct  of  the 
cell  is  given  in  the  table  below.  It  is  to  be  understood  that 
whenever  the  deposition  of  the  membrane  was  suspended  it 
was  placed  in  soak  in  a  solution  of  thymol. 

Maximum  resistance. 

January      25     10.25  A.  M.— 12.47  P.  M.  17,000  ohms. 

2.20  P.  M.—  4.40  P.  M.  19,833 

26  10.37  A.  M.— 12.15  P.  M.  24,777 

27  10.45  A.  M.— 12.46  P.  M.  24,333 

28  10.25  A.  M.— 12.40  P.  M.  27,630 

30  10.05  A.  M.— 12.35  P.  M.  30,790 

2.40  P.  M.—  4.44  P.  M.  33,428 

31  10.20  A.  M.— 12.45  P.  M.     37,666 

2.18  P.  M.—  4.44  P.  M.  38,000 

February      1     10.17  A.  M. —12.44  P.  M.  44,170 

2.15  P.  M.—  4.36  P.  M.  47,200 

2  9.58  A.  M.— 12.43  P.  M.  47,500 

3  10.07  A.  M.— 11.44  A.  M.  46,660 

4  9.57  A.  M.— 12.37  P.  M.  46,500 

6  3.10  P.  M.—  4.30  P.  M.  41,200 

7  11.20  A.  M.— 12.15  P.  M.  46,000 

When  the  above  records  were  compared  with  those  of  the 
deposition  of  the  copper  ferrocyairide  membrane,  it  was  seen 
that  the  conduct  of  these  two  membranes  was  quite  similar. 


21 

EXPERIMENT  I. 

Cell  Coi  was  set  up  for  the  first  measurement  on  Febru- 
ary 7  at  4.15  P.  M.,  a  weight  normal  sugar  solution  being 
used.  Also  hundredth  normal  solutions  of  copper  sulphate 
and  potassium  cobalticyanide  were  used  as  membrane  menders. 
The  temperature  was  15°.  Its  resistance  was  46,000  ohms. 
At  9  P.  M.  the  solution  had  developed  an  osmotic  pressure  of 
.769  atmospheres.  The  pressure  continued  to  increase  slowly 
but  uniformly  until  4.30  P.  M.  on  February  8,  at  which  time 
the  pressure  was  1.71  atmospheres,  which  was  the  maximum 
pressure  for  this  experiment.  It  then  fell  slowly  and  uni- 
formly until  the  cell  was  taken  down  at  9  A.  M.  on  February 
10.  At  this  time  the  pressure  was  1.28  atmospheres.  The 
solution  taken  from  the  cell  showed  a  decided  loss  in  rotation, 
which,  of  course,  indicated  a  dilution.  Subsequently  the 
membrane  was  reinforced  on  six  successive  days,  namely, 
Februray  13,  14,  17,  18,  20  and  21,  on  which  days  the 
maximum  pressures  were  49,565  ohms,  41,429  ohms,  38,000 
ohms,  49,130  ohms,  54,500  ohms  and  50,000  ohms  respectively. 
The  total  time  utilized  in  the  above-mentioned  membrane  re- 
inforcement was  twenty-one  hours. 


EXPERIMENT  II. 

Cell  Coi  was  set  up  on  February  23  at  12.15  P.  M.  with 
a  weight  normal  cane  solution.  The  mercury  in  the  mano- 
meter rose  steadily  until  9  P.  M.  when  a  pressure  of  5.28 
atmospheres  was  reached.  At  10  A.  M.  the  following  day  it 
had  fallen  to  4.30  atmospheres,  at  12.30  P.  M.  it  was  3.93 
atmospheres.  At  5  P.  M.  it  had  again  risen  to  5.538  atmos- 
pheres, but  at  8  P.  M.  fell  to  5.198  atmospheres.  At  9.30 
A.  M.  the  following  day  the  pressure  had  risen  to  7.52  atmos- 
pheres. From  this  time  the  pressure  rose  steadily  until  5 
P.  M.  February  27  when  it  had  reached  8.54  atmospheres. 
However,  the  next  day  at  10  A.  M.  the  pressure  developed 
was  8.56  atmospheres.  From  this  time  the  pressure  rose 
steadily  until  9  A.  M.  on  March  3,  when  it  was  9.17 
atmospheres.  At  12.30  P.  M.  the  same  day  it  had  fallen  to 
9.12  atmospheres.  From  this  point  the  pressure  still  again 
increased  until  12.30  March  4,  when  it  was  9.22  atmospheres'. 
At  5  P.  M.  the  pressure  had  fallen  to  9.11  atmospheres. 
From  this  time  the  pressure  gradually  rose  until  10  A.  M. 
on  March  8  when  the  pressure  was  9.697  atmospheres  which 
was  the  maximum  for  this  experiment.  At  this  time  the  cell 
-was  taken  down  and  soaked  in  a  thymol  solution  for  four 
days.  On  March  12  the  membrane  was  reinforced  for  a  period 


22 

of  one  and  one-half  hours  the  maximum  resistance  being 
26,219  ohms.  On  March  13  the  process  was  repeated  this 
time  developing  a  resistance  of  21,800  ohms.  The  resistance 
of  the  cell  on  the  following  day  after  being  subjected  to  the 
membrane  forming  process  for  a  period  of  five  hours  was 
34,062  ohms.  The  maximum  resistance  on  March  15  after 
the  membrane  had  been  reinforced  for  a  period  of  three  hours 
was  29,460  ohms.  Before  the  cell  was  set  up  on  March  24  the 
membrane  was  reinforced  for  a  period  of  two  hours  the  maxi- 
mum resistance  for  that  time  being  37,667  ohms. 

EXPERIMENT  III. 

Cell  Coi  was  set  up  March  24  at  12.30  P.  M.  with  a 
weight  normal  cane  sugar  solution.  Also  the  usual  solutions 
of  membrane  menders  were  used.  At  9  A.  M.  on  March 
25  there  was  an  osmotic  pressure  of  1.39  atmospheres.  The 
pressure  increased  gradually  for  twenty-four  hours  at  which 
time  it  was  2.49  atmospheres.  During  the  next  twenty-four 
hours  the  pressure  increased  to  18.16  atmospheres.  From  this 
time  9  A.  M.  on  March  27  the  pressure  rose  very  gradually 
until  April  11  when  it  had  reached  24.59  atmospheres,  which 
was  the  maximum  attained  in  this  experiment.  This  pressure 
was  maintained  for  two  days  when  the  cell  was  opened.  The 
cell  was  then  put  to  soak  in  a  thymol  solution  of  the  usual 
concentration.  In  this  experiment  the  pressure  with  one 
exception  increased  uniformly,  and  without  a  break  in  the 
membrane  so  far  as  could  be  observed,  from  the  time  that  it 
was  set  up  until  it  .was  taken  down  which  was  for  a  period  of 
eighteen  days.  This  is  a  decided  contrast  to  the  previous 
experiment  in  which  the  membrane  broke  at  least  six  times  in 
a  period  of  eleven  days,  which  indicates  that  the  membrane 
was  very  much  strengthened  in  the  second  case.  When  this 
cell  was  opened  the  solution  was  found  to  have  lost  decidedly 
in  rotation,  showing  that  the  membrane  had  at  some  period 
leaked.  This  was  the  last  complete  experiment  with  the  Coi 
cell.  It  was  set  up  again  after  the  usual  soaking  and  rein- 
forcing of  the  membrane,  but  when  the  pressure  had  reached 
about  twenty-three  atmospheres  circumstances  made  the  dis- 
continuance of  the  experiment  necessary. 

CELL  CO4. 

As  has  already  been  noted  cell  Cot  was  also  a  new  cell. 
The  preliminary  work  of  removing  the  air  from  the  cell  wall 
was  carried  out  in  the  manner  already  described.     This  re-  , 
quired  approximately  six  hours   during  which  time  61cc.  of 


23 

the  lithium  sulphate  solution  passed  through  the  cell  wall  and 
the  resistance  rose  from  3,562  ohms  to  56,000  ohms.  Several 
hours  were  required  to  completely  remove  the  electrolyte  from 
the  cell. 

On  February  8  the  deposition  of  the  copper  cobalticyanide 
membrane  in  cell  Coi  was  commenced.  A  brief  history  of  this 
process  can  be  best  given  in  the  form  of  a  table,  which  will 
contain  simply  a  statement  of  the  length  of  the  period  of  de- 
position and  the  maximum  resistance  obtained  during  that 
period. 


February 


Maximum  resistance 

8 

11 

.00 

A. 

M 

.—12 

.42 

P. 

M. 

22 

,400  ohms. 

2 

.40 

P. 

M 

.—  4 

.43 

P. 

M. 

34 

,000 

9 

10 

.35 

A. 

M 

.—12 

.40 

P. 

M. 

65 

,294 

10 

11 

.00 

A. 

M 

.—12 

.20 

P. 

M. 

80 

,000 

11 

10 

.50 

A. 

M 

.—12.45 

P. 

M. 

98 

,333 

13 

10 

.14 

A. 

M 

.—12 

.20 

P. 

M. 

162 

,857 

2 

.50 

P. 

M 

.—  4 

.40 

P. 

M. 

162 

,857 

14 

10 

.19 

A. 

M 

.—12 

.37 

P. 

M. 

145 

,000 

2 

.27 

P. 

M 

.—  4 

.42 

P. 

M. 

145 

,000 

15 

10 

.50 

A. 

M 

.—11 

.40 

A. 

M. 

114 

,000 

It  will  be  noticed  on  comparing  the  above  records  with 
those  for  cell  Coi  that  the  resistance  rose  much  faster  in  the 
latter  case  than  in  the  former.  The  explanation  for  this  may, 
perhaps,  be  that  there  was  a  difference  in  the  porosity  of  the 
cell  walls.  However,  later  work  showed  the  membranes  in 
both  cells  to  be  quite  satisfactory. 


EXPERIMENT  I. 

Cell  Co4  was  set  up  February  15  at  12  M.  with  a 
weight  normal  sugar  solution,  the  temperature  being  15°. 
The  final  resistance  of  the  membrane  was  114,000  ohms.  The 
mercury  in  the  manometer,  so  far  as  it  was  observed,  rose 
continuously.  At  9  P.  M.  the  solution  had  developed  a  press- 
ure of  5.95  atmospheres.  The  following  day  at  9  A.  M.  it 
was  7.01  atmospheres,  which  was  the  maximum  developed 
during  this  experiment.  After  this  time  the  pressure  fell 
slowly  for  forty -eight  hours,  at  which  time  the  cell  was  opened, 
the  pressure  then  being  3.60  atmospheres.  The  cell  was  then 
soaked  in  thymol  solution  for  two  days,  after  which  the  mem- 
brane was  reinforced  on  three  successive  days.  The  maxi- 
mum resistances  obtained  were:  15,571  ohms,  13,750  ohms 
and  110,000  ohms  respectively. 


24 

EXPERIMENT  II. 

Cell  Co4  was  set  up  on  February  23  at  12.15  P.  M.  with 
a  weight  normal  sugar  solution.  The  final  resistance  of  the 
membrane  was  110,000  ohms.  At  9  P.  M.  the  membrane  had 
developed  a  pressure  of  5.323  atmospheres.  The  pressure  at 
10  A.  M.  the  following  day  had  dropped  to  3.15  atmospheres. 
Subsequently  it  rose  gradually  for  forty-eight  hours,  at  the 
expiration  of  which  time  it  was  12.10  atmospheres.  The 
pressure  then  fell  to  11.84  atmospheres,  after  which  it  rose 
again  very  uniformly  for  eleven  days  to  20.64  atmospheres. 
The  cell  was  then  taken  down  and  placed  to  soak  in  the  usual 
thymol  solution.  The  solution  taken  from  the  cell  was  some- 
what diluted,  as  shown  by  its  loss  in  rotation.  After  the 
membrane  had  been  soaked  in  the  thymol  solution  for  a  period 
of  three  days  it  was  reinforced  in  the  usual  manner  on  four 
successive  days,  the  maximum  resistances  for  these  periods 
being  66,875  ohms,  90,835  ohms,  109,000  ohms  and  109,000 
ohms  respectively. 

EXPERIMENT  III. 

Cell  Co4  was  set  up  March  1 5  with  a  weight  normal  sugar 
solution,  the  resistance  of  the  membrane  being  109,000  ohms. 
The  pressure  developed  at  8  P.  M.  was  1.17  atmospheres.  The 
following  day  at  9  A.  M.  the  pressure  had  risen  to  8.32  atmos- 
pheres. During  the  next  three  hours  it  increased  to  12.60 
atmospheres.  At  5  P.  M.  the  pressuse  was  17.23  atmospheres. 
From  this  time  the  pressure  rose  uniformly  for  eight  days,  at 
the  end  of  which  time  it  was  25.29  atmospheres.  After  it  had 
remained  practically  constant  at  that  point  for  three  days  the 
cell  was  taken  down  and  placed  in  a  thymol  solution.  After 
the  cell  had  soaked  in  the  thymol  solution  for  two  days  the 
membrane  was  again  reinforced  at  three  separate  periods,  the 
total  time  of  which  was  three  and  a  half  hours.  During  this 
time  the  maximum  resistance  obtained  was  95,833  ohms. 


EXPERIMENT  IV. 

On  April  20  at  12  M.  Cell  Co4  was  set  up  for  the 
fourth  time  with  weight  normal  cane  solution.  At  first  the 
pressure  rose  slowly  being  at  10  A.  M.  the  following  day 
only  1.04  atmospheres.  Seven  hours  later  it  was  only  1.50 
atmospheres.  During  the  following  day  the  pressure  rose 
from  3.69  atmospheres  at  9  A.  M.  to  6.87  atmospheres  at 
5  P.  M.  However,  during  the  following  night  it  rose  from 
a  pressure  of  6.87  atmospheres  to  one  of  24.02  atmospheres. 
During  the  following  two  days  it  rose  slowly  but  uniformly  to 


25 

26.516  atmospheres.  This  being  the  maximum  pressure 
obtained  during  the  experiment.  Also  it  was  the  maximum 
pressure  obtained  during  the  investigation  of  the  copper 
cobalticyanide  membrane.  The  pressure  obtained  from  a  large 
number  of  experiments  with  other  membranes,  at  this  tempera- 
ture and  concentration  of  solution,  has  been  shown  to  be 
27.223  atmospheres.  The  solution  taken  from  the  cell  showed 
some  loss  in  rotation.  The  leakage  of  the  membrane  pro- 
bably occured  during  the  early  part  of  the  experiment  when 
the  increase  in  the  osmotic  pressure  was  very  slow. 

CONCLUSIONS. 

In  this  investigation  of  the  copper  cobalticyanide  mem- 
brane, it  has  been  shown  that  although  it  is  not  as  active  at 
first,  as  the  nickel  ferrocyanide  membrane,  it  however 
promises  to  be  very  satisfactory.  This  membrane  appears  to 
be  quite  similar  in  its  behavior  to  the  copper  ferrocyanide 
membrane.  In  the  initial  deposition  of  both  membranes  it 
has  been  found  that  the  rise  in  resistance  of  the  membrane  is 
very  much  slower  than  in  the  case  of  zinc  and  nickel  ferro- 
cyanides.  However,  this  rise,  in  the  case  of  both  the  cobalti 
and  ferrocyanides  of  copper  is  very  uniform.  Also  this  mem- 
brane like  that  of  the  copper  ferrocyanides  when  set  up  for 
the  first  measurements  failed  to  give  very  high  pressures. 
However,  both  membranes  have  been  shown  to  give  higher 
and  higher  prsssures  on  each  succeeding  time  of  setting  up 
for  a  measurement. 

Since  the  results  obtained  with  the  copper  cobalticyanide 
membrane  during  this  investigation  have  proved  so  promising 
it  is  to  be  expected  that  it  will  be  found  useful  in  the  exact 
measurement  of  osmotic  pressure.  It  is  to  be  regretted  that 
it  was  necessary  to  suspend  temporarily  the  investigation  of 
the  membrane.  However,  the  investigation  will  soon  be 
resumed.  It  was  to  be  expected  in  the  light  of  the  past 
experiment  that  one  or  two  further  reinforcements  of  the 
membrane  would  put  it  in  good  condition  for  the  accurate 
measurement  of  osmotic  pressure. 


REMOVAL  OF  MEMBRANES. 

After  membranes  have  been  reinforced  many  times  and 
have  been  in  use  from  twelve  to  eighteen  months  they  become 
thickened  to  such  an  extent  that  water  passes  through  them 
very  slowly  at  ordinary  temperature  and  a  measurement  of 
osmotic  pressure  therefore  requires  a  very  long  time.  For  the 
same  reason  these  old  cells  are  peculiarly  subject  to  what  is 


26 

known  as  "thermometer  and  barometer"  effects.  Such  mem- 
branes become  more  active  at  higher  temperatures  and  can 
still  be  used  at  these  temperatures  with  advantage.  It  is 
nevertheless  highly  desirable  that  these  membranes  be  re- 
moved and  substituted  by  new  and  more  active  ones.  One 
great  disadvantage  of  the  use  of  cells  with  thick  and  too  slow 
membranes  is  the  fact  that  when  used,  they  monopolize  for 
long  periods  the  rather  limited  bath  space. 

Previously,  the  cells  containing  membranes  in  this  condi- 
tion were  discarded  except  for  high  temperatures,  since  at- 
tempts to  remove  them  and  substitute  other  membranes  had 
not  been  wholly  successful.  At  first  it  was  attempted  to 
remove  these  membranes  by  dissolving  with  mineral  acids. 
Ivater  ammonia,  amtnonical  solution  of  tartaric  acid,  and  a 
solution  of  Rochelle  salts  were  employed  as  solvents.  Still 
later  the  membrane  was  removed  by  electrolysis  in  the  pres- 
ence of  tartaric  acid.  But  in  all  cases  the  new  membrane 
which  was  substituted  for  the  older  one  was  found  to  be  de- 
fective. The  reason  for  this  could  not  be  ascertained.  It 
was  suggested,  however,  that  the  openings  of  the  pores  into 
which  it  is  necessary  for  the  membranes  to  root  themselves  for 
support,  had  in  some  way  become  modified  by  the  reagents  so 
that  the  membranes  no  longer  were  as  firmly  attached  to  the 
cell  wall  as  they  are  in  new  cells.  In  view  of  this  explanation  it 
was  suggested  that  perhaps  success  could  be  attained  by  me- 
chanically grinding  away  a  portion  of  the  inner  surface  of  the 
cell  wall,  on  which  the  membrane  is  located. 

To  accomplish  this  a  small  high-speed  emery  wheel, 
mounted  on  a  mandrel,  was  used.  At  intervals  the  grinding 
was  discontinued  and  the  interior  of  the  cell  carefully  exam- 
ined by  means  of  a  two- volt  lamp,  which  was  so  mounted  as  to 
allow  it  to  be  introduced  to  the  very  bottom  of  the  cell.  After 
it  appeared  that  the  membrane  had  been  removed  from  every 
part  of  the  interior,  the  grinding  was  discontinued  and  the 
cells  placed  to  soak  in  distilled  water. 

When  it  had  been  shown  that  the  zinc  ferrocyanide  mem- 
brane was  valueless  as  a  medium  for  the  measurement  of 
osmotic  pressure,  the  two  cells  in  which  that  membrane  had 
been  deposited  were  treated  in  the  manner  described  above. 
After  the  cells  had  been  soaked  for  a  time  in  distilled  water 
they  were  subjected  to  endosmose  with  a  .005  normal  lithium 
sulphate  solution  to  remove  the  air,  as  well  as  any  particles 
which  may  have  gotten  into  the  pores  of  the  cell  wall  during 
the  grinding.  With  this  treatment  the  platinum  electrode  on 
the  interior  of  the  cell  became  darkened,  due  to  a  deposition  of 
zinc,  and  the  exterior  of  the  cell  became  colored  blue,  due 
probably  to  complex  cyanogen  compounds.  This  showed  that 


27 


there  were  still  roots  of  the  membrane  in  the  cell  wall.  Con- 
sequently the  zinc  was  dissolved  from  the  electrode  by  nitric 
acid.  The  lithium  sulphate  solution  was  renewed  and  the 
current  again  turned  on,  this  time  passing  in  the  reverse  di- 
rection, so  that  the  zinc  ion  was  carried  to  the  exterior  of  the 
cell,  and  at  the  same  time  the  ferrocyanogen  ion  was  carried 
to  the  interior.  The  endosmose  with  the  lithium  sulphate 
solution  was  continued  as  long  as  there  was  any  deposition  of 
zinc  on  the  exterior  electrode.  When  this  point  was  reached 
it  was  considered  that  the  last  traces  of  the  zinc  ferrocyanide 
membrane  had  been  removed. 

Since  the  nickel  ferrocyanide  membrane  had  given  very 
satisfactory  results  it  was  thought  best  to  deposit  this  mem- 
brane in  these  cells  and  thus  to  test  their  efficiency.  The 
nickel  ferrocyanide  membranes  were  deposited  and  developed 
in  these  cells  in  the  manner  already  described.  When  suffi- 
cient membrane  had  been  deposited  and  the  resistance  of  the 
cells  had  reached  a  maximum  they  were  set  up  for  measure- 
ments. A  complete  record  of  the  results  obtained  with  this 
membrane  has  been  given  under  the  discussion  of  the  zinc 
ferrocyanide  membrane.  The  results  there  recorded  leave  no 
doubt  that  the  old  membranes  may  be  successfully  dealt  with 
in  the  manner  described. 


BIOGRAPHICAL. 

The  author  was  born  at  Walpole,  N.  H.,  July  19,  1884. 
His  early  education  was  received  in  the  public  schools  of  his 
native  town.  In  September  1902  he  entered  Darmouth  College, 
from  which  he  graduated  in  1906,  with  the  degree  of  Bachelor 
of  Science.  The  following  year  he  was  instructor  of  chemis- 
try at  the  University  of  Maine.  At  the  close  of  1907  he  was 
appointed  instructor  of  chemistry  at  Massachusetts  Agricul- 
tural College,  where  he  remained  one  year.  In  the  fall  of 
1908  he  entered  the  graduate  department  of  Johns  Hopkins 
University  making  chemistry  his  principal  subject,  and  physi- 
cal chemistry  and  minerology  first  and  second  subordinate 
subjects,  respectively. 

In  the  year  1909-10  he  was  assistant  to  Dr.  Gilpin  and  in 
the  year  1910-11  assistant  to  Professor  Renouf. 


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